Although our Perl client library is free, the server-side code is proprietary.

> and how does one avail of the data it provides?

We sell rsync access to our lists. We also provide it for free to our
CanIt customers. Finally, we have reciprocal arrangements with some
large email users who get rsync access to the lists in return for
reporting data back to us. For more info, please see
http://www.roaringpenguin.com/products/canit-reputation-rbl